1. Field of the Invention
The present invention relates to speech processing. More specifically, the invention relates to a method and apparatus for enhancing 3-D (three-dimensional) localization of speech.
2. Description of Related Art
Normal human speech contains a wide range of frequency components, usually varying from about 100 Hz (hertz) to several KHz (kilohertz). For instance, human speech has a low frequency fundamental, but the harmonics of human speech has a fairly wide scale. Due to the wide range of frequencies found in human speech, one is able to localize a source of speech when one is speaking to someone. In other words, one is generally able to locate and identify the source of speech with a particular individual.
In order to determine the intelligibility or message of the speech, a listener does not require the higher-frequency components contained in the speech. Therefore, many communication systems, such as cellular phones, video phones and telephone systems that use speech compression algorithms, discard the high-frequency information found in a speech source. Thus, most of the high-frequency content above 4 kilohertz (KHz) is discarded. This solution is adequate when localization of the speech is not needed. But for applications that require or desire localization of the speech (e.g., virtual reality), the loss of the high-frequency components of the speech proves to be detrimental. This is because the higher-frequencies are required for speech localization by a listener. The high-frequency content in speech helps a listener to mentally perceive where a sound is located. For instance, it helps the listener determine whether a sound is located above or below the listener, or to the right or to the left, or in front of or in back of the listener. Thus, what is needed is a method of converting speech that has been transmitted through a communication system that discarded its high-frequency content. This method should allow a listener to localize the converted speech without losing any intelligibility in the speech.